A complex embedded system is characterized as involving numerous elements in the operating interface, among which are lots of irregularly shaped graphic elements. There exists a need to properly display these elements.
Currently there are mainly two solutions:
One is to arrange the graph layering in advance. Specifically, different image elements are first assigned to different graphic layers in accordance with circumstances. When they are converted to video signals for output, the content in each graphic layer is combined into a single pixel value (grayed or colored) and outputted to a display device. Mindray Co. has got a patent for this method, see the patent application No. 03113847.0, entitled “Method and Circuit for Real-Time Waveform Smooth Scroll and Background Image superposition display”, by Mu Lemin.
Another method is that all graphic elements are directed from top to bottom to the same graphic layer instead of being grouped into different layers. However, when the content of one of the sparse graphs is changed, all of the superposed parts of the sparse graph have to be re-plotted from top to bottom.
The method of arranging graphic layers in advance may solve the flickering problem, but the biggest problem with this method is that the system using this method provides poor flexibility. When display requirements (e.g., upper and lower layout) are changed, it is required to rearrange and redesign the display. Though the flexibility may be improved by means of software, the display speed will be rather slow, and it is difficult to achieve a faster refresh rate for display (i.e., lower frame rate) in common embedded systems. Satisfactory visual effect can be achieved only if the graph layering is implemented by means of hardware, but this will increase manufacture and maintenance cost.
Redrawing an overlapped sparse graph may be conveniently implemented by means of software. However, this method needs to deal with the conflict between display effect and display speed. Since all of the sparse graphs on the sparse graph to be refreshed have to be refreshed, flicker is caused with regard to the display effect, which cannot be avoided even if a fast refresh rate of the video memory is used. One of the common anti-flicker measures is a dual buffer scheme, according to which the plotting is first finished in a memory and then directly on the screen. However, this will increase the time for plotting, thus causing the response performance of the embedded system to decrease.